We plan to continue a long-term research program aimed at advancing and applying fundamental knowledge in the fields of respiratory mechanics and control. We present six interrelated projects: 1. Micro-mechanics of the lung - description of the extent, pattern and functional significance of local non-uniformities in lungs. 2. Airway aerodynamics - development and testing of theoretical predictions of flow-limitation and of frequency response in airways. 3. Chest wall mechanics and mechanical factors in the control of breathing -explanation of the mechanisms of mechanical interaction between the diaphragm and rib cage and definition of the neural mechanisms responsive to shifts in operating lengths of respiratory muscles. 4. Comparative mammalian respiratory mechanics - study of respiratory physiology in mammals over a wide range of size, behavior and habitat, with emphasis on respiratory mechanics. 5. Development and evaluation of tests of pulmonary function - emphasis being placed on improved methods for assessing forced expirations and frequency response of airways. 6. Mechanisms of bronchial reactivity - to acute and chronic airway challenge in the dog: physiologic, pharmacologic and morphologic correlation. The methods to be used include: measurements of pressures, volumes, flows, linear dimensions, electromyographic activity, gas composition, x-ray density, radioactive tracers; and development of mathematical models to be tested with observations made on normal and abnormal humans and other mammals.